1. Field of the Invention
The present invention relates to a defect inspection method and defect inspection apparatus, and more particularly to a defect inspection method and defect inspection apparatus employing detection of defect circuit on patterns formed on samples, such as photomasks and reticles used for semiconductor manufacturing as well as liquid crystal display or the like.
2. Discussion of the Background
Semiconductor integrated circuits are manufactured by repeating several process steps of transferring a circuit pattern from a reticle onto a wafer that acts as an original place through reduction exposure of the pattern using ultraviolet rays or deep ultraviolet rays of light.
Present day innovations in performance of DRAMs and MPUs are mostly due to innovations in microfabrication technology of semiconductor integrated circuits. And an advance in the microfabrication technology will be in more need to meet the demands for achieving of a further increase in performance. For example, in regard to the quality of reticles, position accuracy, improve size accuracy, and decrease or eliminate killer defects are becoming more demanding than ever before. As reticle fabrication technology is improved such as circuit pattern drawing transfer techniques, mask process and the like, it will be strictly required that product-test/inspection techniques should be likewise improved to guarantee the final quality of such manufactured reticles.
For detection of defects on the reticles, it is necessary to detect CD (critical dimension) defects of patterns in addition to defects of patterns including pin dots, pinholes and equivalents thereto. For a pattern of contact holes which have rectangular opening sections, detection of defects becomes especially important in view of the fact that these defects can greatly affect the dimension or size of a transferred pattern being formed on a wafer. For example, it is considered that the design role for DRAMs of the 1-gigabit generation will be as small as 150 nm on wafers, that is 600 nm on the quadric magnification (4xc3x97) reticles. In this respect, more strict specifications are considered to be required to the extent that the CD error should be less than 20 nm, which will be equivalent to a value of 3% or less after conversion to transmission errors of the openings of contact holes.
The above-mentioned issue is not limited to the contact holes but also holds true of patterns of lines-and-spaces.
Furthermore, since small auxiliary patterns which are used in optical proximity effect correction (OPC) such as jogs, serifs and equivalents thereof are incapable of obtaining the intended optical images with a sufficient resolution, the measurement errors can further increase in case of samples which employ these auxiliary patterns.
As described above, the prior technique is encountered with more difficulty in detecting the CD defects in the patterns of contact holes and lines-and-spaces with high accuracy and sensitivity, as these patterns decrease in size. In addition, for these patterns containing therein small serifs and jogs or the like for effectuation of optical proximity effect correction (OPC), it is becoming more and more difficult to detect their defects with high accuracy and sensitivity.
The present invention has been made in view of the above, and its primary object is to provide a defect inspection method and defect inspection apparatus which is capable of detecting defects accurately and sensitively in a pattern.
In order to attain the foregoing object, the present invention employs a specific configuration which follows.
In summary, the present invention is directed to a defect inspection method for detecting defects of a pattern formed on a sample, comprising the steps of inputting an optical image of the sample as sensor data, inputting reference data corresponding to the sensor data, calculating a transmission error and a displacement of the sensor data based on the sensor data and the reference data, and analyzing a defect of the sample from the transmission error and the displacement of the sensor data.
In the method, the sensor data can be extracted from inspection regions pursuant to a size and a shape of the pattern, and the reference data can be extracted in accordance with the extracted sensor data. And the analyzed defect can be at least one of the group consisting of a transmission defect, a critical dimension (CD) defect, and a relative displacement defect.
This invention is also directed to a defect inspection method for detecting defects of a pattern formed on a sample, comprising the steps of inputting an optical image of the sample as sensor data inputting reference data corresponding to the sensor data, calculating a first transmission error and a first relative displacement of the sensor data based on the reference data, performing position alignment of the sensor data and the reference data based on the calculated the first relative displacement, calculating a second transmission error and a second relative displacement using the aligned reference data and the aligned sensor data, and analyzing a defect of the sample from the second transmission error and the second displacement of the sensor data.
In the method, the sensor data can be extracted from inspection regions pursuant to a size and a shape of the pattern and the reference data can be extracted in accordance with the extracted sensor data. And the analyzed defect can be at least one of the group consisting of a transmission defect, a critical dimension (CD) defect, and a relative displacement defect.
In the above inventions, a step of inputting inspection region data can be added designating a plurality of inspection regions of the sample in conformity with the size and shape of the pattern. Also, a step of searching for a to-be-inspected pattern with respect to the reference data can be added.
Here, the step of inputting the inspection region data can input a rectangular region including at least one opening section as the inspection region. And the step of inputting the inspection region data can input the inspection region as an array of rectangular regions, a center of gravity of the rectangular region being substantially identical to that of the opening section, and the rectangular region excluding another opening section which is adjacent to the opening section.
Furthermore, if the opening section is a contact hole, and the step of calculating the transmission error and the displacement of the sensor data can include a step of solving the equation:
xcex5xc2x7U(x,y)+x0xc2x7dU/dx+y0xc2x7dU/dy=U(x,y)xe2x88x92S(x,y)
where S(x,y) is the sensor data at at least three independent coordinates (x,y), U(x,y) is the reference data, dU/dx is an X direction differential value of the reference data, and dU/dy is a Y direction differential value of the reference data, with the transmission error xcex5 and the relative displacement x0, y0 being as an unknown quantities. Here, the step of calculating the transmission error and the displacement of the sensor data can include a step of solving the equation using a least square method at those coordinates excluding an area of the rectangular region corresponding to the interior of a light shield section of the sample.
Similarly, if the opening section has lines-and-spaces, and the step of calculating the transmission error and the displacement of the sensor data can include a step of solving the equation:
xcex5xc2x7U(x,y)+l0xc2x7dU/dl=U(x,y)xe2x88x92S(x,y)
where S(x,y) is the sensor data at at least two independent coordinates (x,y), U(x,y) is the reference data, and dU/dl is a differential value of the reference data in a direction perpendicular to said lines-and-spaces, with the transmission error xcex5 and the relative displacement l0 being unknown quantities. Here, the step of calculating the transmission error and the displacement of the sensor data can include a step of solving the equation represented above using a least square method at those coordinates excluding an area of the rectangular region corresponding to the interior of a light shield section of the sample.
The present invention is further directed to a defect inspection apparatus for detecting defects of a pattern formed on a sample, comprising a sensor data memory for storing an optical image of the sample as sensor data, a reference data memory for storing reference data corresponding to the sensor data, a calculator for calculating a transmission error and a displacement of the sensor data based on the sensor data stored in the sensor data memory and the reference data stored in the reference data memory, and a defect analyzer for analyzing a defect of the sample from the transmission error and the displacement calculated by the calculator.
In the apparatus, the sensor data can be extracted from inspection regions pursuant to a size and a shape of the pattern, and the reference data can be extracted in accordance with the extracted sensor data. Also, the defect analyzed by the defect analyzer can be at least one of the group consisting of a transmission defect, a critical dimension (CD) defect, and a relative displacement defect.